This invention relates to a novel surgical device scalable to small dimensions for thermally-mediated treatments or thermoplasties of targeted tissue volumes. An exemplary embodiment is adapted for shrinking, sealing or welding tissue. The instrument and technique utilize electrical energy to instantly convert a biocompatible fluid media to a superheated media, perhaps a gas media, within an electrically insulated instrument working end. The altered media is characterized by a (i) a high heat content, and (ii) a high exit velocity from the working end""s tissue engagement plane. Both of these characteristics are controlled to hydrate tissue while at the same time denaturing proteins to shrink, seal, weld or cause any other thermally-mediated treatment of an engaged tissue volumexe2x80x94and while causing limited collateral thermal damage and totally eliminating electrical current flow in the engaged tissue volume.
Various types of laser and radiofrequency (Rf) surgical instruments have been developed for delivering thermal energy to tissue, for example to cause hemostasis, to weld tissue or to cause a thermoplastic remodeling of tissue. While such prior art forms of energy delivery work well for may applications, laser and Rf energy typically cannot cause highly localized thermal effects that are desirable in microsurgeries or other precision surgeries.
Laser and Rf energy applications cause thermal effects in tissue based on different principles. In general, the non-linear or non-uniform characteristics of tissue affect both laser and Rf energy distributions in tissue. For example, FIG. 1A shows a typical pattern of energy distribution and resultant thermal effects in a prior art laser irradiation of tissue. The cross-section of the energy emitter or emission is indicated at ee at the tissue interface wherein a fiber optic interfaces tissue of a light beam strikes the tissue. In the case of a suitable infrared laser emission, water in tissue comprises a chromophore to absorb photonic energy resulting in a thermal effect. The turbidity of tissue scatters photons, and the resulting thermal effect is indicated by arbitrary isotherms 100, 80 and 60 which for example indicate degrees in centigrade. FIG. 1A shows that tissue desiccation d at the surface will occur to prevent photon transmission after an certain interval of energy delivery. If the objective of the thermal therapy in FIG. 1A were to seal or weld tissue, which is assumed to require a threshold temperature of 80xc2x0 C., it can be seen that deeper tissue indicated at b may not reach the threshold welding temperature before the tissue surface is desiccated. Further, it can be seen that collateral tissue indicated at c may be sealed or welded, even though such tissue is collateral to the cross-section of the energy emission ee.
FIG. 1B next shows a typical energy distribution pattern when using a prior art bi-polar Rf energy delivery. In this schematic illustration, the cross-section of the energy emitter is again indicated at ee which defines the interface between a tissue surface and the electrodes 4a and 4b. As the electrodes are energized from an electrical source, the current flows are in constant flux and flow through random paths of least resistant between the electrodes. The tissue is elevated in temperature by it resistance to current flow, resulting typically in tissue desiccation or charring d at the electrode-tissue interface. When tissue in contact with the electrode is entirely desiccated, the current flow between the electrodes terminates. As represented in FIG. 1B, thermal effects typically occur in regions of tissue (indicated at c) collateral to the targeted tissue between the electrodes. Further, the prior art Rf energy delivery of FIG. 1B causes stray Rf flow collateral tissues that may be undesirable.
What is needed is an instrument and technique (i) that can controllably deliver thermal energy to non-uniform tissue volumes; (i) that can shrink, seal or weld selected tissue volumes without desiccation or charring of proximate tissue layers; (iii) that can shrink, seal or weld a targeted tissue volume while preventing collateral thermal damage; and (iv) that does not cause stray Rf current flow in tissue.
The present invention is adapted to provide novel systems and techniques capable of controlled thermal energy delivery to localized tissue volumes, for example for sealing, welding or thermoplastic remodeling of tissue. Of particular interest, the system can create thermal welds or seals in a targeted tissue without the use of Rf current flow through the patient""s body, which is typical in the prior art. The systems and techniques are particularly adapted for sealing or welding thick tissue and non-uniform tissue layers. The biological mechanisms underlying tissue fusion or welding are complex and are not fully understood. Application of thermal energy can be used to elevate tissue temperatures to the level that causes denaturation of proteins, which is a first step in tissue fusion. The terms fuse, weld and seal are used interchangeably herein, mean that a temperature-induced protein denaturation process causes such proteins (particularly various types of collagen), water and other tissue constituents to meld into a proteinaceous amalgam. Such a form of thermal biological glue occurs at temperatures ranging from about 65xc2x0 C. to 100xc2x0 C. Upon the cooling of tissue and subsequent healing of the treated tissue, the tissue is fused together or welded as the damaged proteins re-nature in a part of the body""s wound healing process.
The probe of the present invention has a working end that defines a tissue-contacting surface or engagement plane with a plurality of media entrance ports that enter the engagement plane. A fluid media source is fluidly coupled to the media entrance ports by a fluid channel. Fluid vaporization means, for example comprising paired electrodes, are carried within the channel for converting the fluid media from a first liquid state to a second gas statexe2x80x94i.e., a flash vaporization means. The instrument and technique thus utilize electrical energy to convert the biocompatible fluid media to a superheated gas media that has a high heat content that enters the engagement plane at velocity and penetrates into the targeted tissue.
In a further embodiment of the invention, the tissue-contacting surface may carry components of a sensor system which together with a power controller can control the intervals of electrical discharges during a thermotherapy. For example, feedback circuitry for measuring temperatures at one or more temperature sensors may be provided. The power controller can also modulate and control voltage of the discharge to alter media exit velocity, all in order to achieve (or maintain) a particular parameter such as a particular temperature in tissue, an average of temperatures measured among multiple sensors, or a temperature profile (change in energy delivery over time).
The instrument and method of the invention advantageously cause thermal effects in tissue that do not rely applying an electrical field across the tissue to be treated.
The instrument and method of the invention advantageously cause thermal effects in tissue that do not rely delivering high-intensity laser energy to the targeted tissue.
The instrument and method of the invention creates thermal effects in targeted tissue that without causing tissue desiccation or surface carbonization common to electrosurgical modalities and laser irradiation modalities.
The instrument and method of the invention advantageously creates thermal effects in a targeted tissue volume with substantially controlled lateral margins between the treated tissue and untreated tissue.
The instrument and method of the invention creates thermal effects in targeted tissues that caused stray electrical current flow in the patient""s body.
Additional advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.